This application claims the priority of Korean Patent Application No. 2002-64345, filed on Oct. 21, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission device, and more particularly, to a field emission device having improved electron emission efficiency, brightness, color purity, and durability due to a focusing electric field.
2. Description of the Related Art
As shown in FIG. 1, in a field emission device (FED) using carbon nanotubes (CNTs), a cathode 2 is formed on a substrate 1, and a gate insulating layer 3 is formed on the cathode 2. The gate insulating layer 3 has a well 3a that exposes a portion of the cathode 2. An electron emitter 4 is formed of carbon nanotubes on the exposed portion of the cathode 2. A gate electrode 5 with a gate hole 5a corresponding to the well 3a is formed on the gate insulating layer 3.
A process of manufacturing a conventional FED having the above-described structure will be described in brief with reference to FIGS. 2A through 2J.
As shown in FIG. 2A, a cathode 2 is formed of a transparent conductive material such as ITO on a substrate 1 made of glass. Actually, a plurality of cathodes 2 are formed in parallel strips. To form the cathode 2, a process of depositing ITO on the entire surface of the substrate 1 and patterning the ITO is performed.
Referring to FIG. 2B, a first insulator 3′ is coated on the cathode 2, and then heated. Thereafter, a second insulator 3″ having a lower etching rate to an etchant than the first insulator 3′ is coated on the first insulator 3′, and then heated. As a result, a gate insulating layer 3 having a thickness of about 10 microns is completed.
As shown in FIG. 2C, chromium (Cr) is deposited on the gate insulating layer 3 to form a gate electrode 5.
As shown in FIG. 2D, a photoresist layer 6 is coated on the gate electrode 5. Thereafter, as shown in FIG. 2E, the photoresist layer 6 is patterned to form a window 6a corresponding to a gate hole 5a and a well 3a in the photoresist layer 6. Next, a portion of the gate electrode 5 exposed by the window 6a is dry etched.
Referring to FIG. 2F, an etchant is supplied through the window 6a to etch the gate insulating layer 3. Here, since the first insulator 3′ of the gate insulating layer 3 has a higher etching rate than the second insulator 3″ of the gate insulating layer 3, the well 3a shown in FIG. 2F is formed.
As shown in FIG. 2G, the gate electrode 5 is patterned to broaden the gate hole 5a. Due to patterning of the gate electrode 5, the gate electrode 5 on the gate insulating layer 3 is divided into a plurality of gate electrodes which are arranged in parallel strips.
Referring to FIG. 2H, a photoresist 7 is properly coated on the gate electrode 5, and then patterned so that a portion of the cathode 2 in the center of the floor of the well 3a is exposed.
As shown in FIG. 2I, a CNT paste 4a containing photoresist is coated on the photoresist 7. Here, the CNT paste 4a fills the well 3a. 
Referring to FIG. 2J, an exposure and development process is performed using a pattern mask (not shown) so that the CNT paste 4a remains in the center of the floor of the well 3a. As a result, an electron emitter 4 is formed on the cathode 2.
Through the above-described process, a lower substrate including an electron gun structure having a cathode, a gate electrode, and so forth is completed. Next, the lower substrate is heated, and then sealed to a front substrate, which is coated with R, G, and B fluorescent materials, with a predetermined gap between the two substrates.
In the electron gun structure shown in FIG. 1 or FIG. 2J, an electron beam emitted from the electron emitter 4 diverges due to mutual repulsion of electrons in the electron beam and a strong electric field is formed by applying a positive voltage to the gate electrode 5. As a result, the electron beam is defocused, which increases the size of a spot formed on the fluorescent material. Then, the electron beam lands on other regions adjacent to its intended target fluorescent material. Thus, color purity is degraded, which results in poor image quality. Also, as the positive voltage of the gate electrode 5 increases, the electron beam further diverges after exiting the gate hole 5a. Thus, most of the intensity of the electron beam radiated onto a fluorescent material is at the periphery of a corresponding pixel. If divergence of the electron beam is not minimized, load on the electron emitter 4 increases during high current driving or a long driving period, thereby reducing the life span of the electron gun structure.
These problems occur in a spint type FED using metal micro tips as an electron emitter. Thus, for the spint type FED, a method of forming a double gate was introduced in order to reduce divergence of the electron beam. However, as is known, the spint type FED has a complicated structure, is not suitable as a wide-screen FED, and is expensive.